| With the power lines spreading all over the city and countryside, it has constituted the biggest network in the world. Using power lines for high speed data communication is convenient for automation and information system of power systems. Moreover it provides a convenient, fast, economical and reliable connection mode for 'the last one miles" problem of Internet wide band connection and indoor interconnections. However, power line channel has some characteristics to hinder data communication, such as strong noise, much attenuation of high frequency signal, serious multi-path disturbance. The current used wide band power line communication equipments have some limitations, such as instable communication speed, high hardware cost etc. Also, the radiation of high frequency signal in the power line can disturb wireless communication, which is another limitation for the development of power line communication.To deal with the above problems, the following research is finished in this thesis:(1) To overcome the shortcomings caused by strong noise of the power line channel and the dramatic variety of the input impedance, an improved power line optimization device is designed in this thesis. Verified by calculation and simulation, the device can not only filter the high frequency noise in the channel, but also realize the function of impedance matching which can not be realized by the present power line channel optimization device. It can optimize channel and improve signal-to-noise ratio and channel capacity.(2) In order to keep the integrity of received signals, it is proposed in this thesis to adopt reverse symmetry input method to conquer the crosstalk between lines, based on the analysis of the multi-conductor transmission line crosstalk. Simulation indicates that the method has obvious advantages in the aspect of restraining crosstalk and stabilizing signal comparing with the traditional signal transmission. Therefore, it can improve the amplitude of the received signal. Moreover, the similarity of noise in the multi-conductor is discussed, and the possibility of eliminating noise with the reverse symmetry input method is analyzed.(3) With the purpose of improving the channel capacity, the modulation and demodulation mode of multi-conductor transmission line transmit signal in parallel are studied. The problem to be solved is how to avoid the confusion of the received signal caused by the crosstalk between multi-line parallel signals. In this thesis a combination of the OFDM and ICA is used to convert the complicated convolution-type ICA to the mode applied to simple instantaneous-liner-mixed system. The general steps and mathematical form of the modulation and demodulation are discussed and the feasibility of the method is demonstrated.(4) High frequency signals transmitting in the power line may result in comparatively strong electromagnetism radiation and will disturb the wireless communication. In order to avoid the problem, based on the comparison of the power line and telephone line, ADSL2+ technology is proposed in this thesis to realize wide band power line communication based on the power line channel optimization device. The simulation result indicates that between the frequence of 0-2.2MHZ applied by the ADSL2+, the signal of power line attenuates little, the influence of crosstalk is not serious and the multi-path disturbance will not cause evident frequency-switching attenuation. Therefore, adopting the method can not only alleviate electromagnetism radiation, but improve communication performance. |
